Web advance mechanism

ABSTRACT

Web advancing mechanism suitable for use in, for example, a low cost strip printer. A pair of torsion springs surround a cylindrical capstan. A free end of each spring is attached to a member which applies torque to the springs to urge the capstan into contact with the web. An advance mechanism causes the capstan to be incrementally rotated in one direction to advance the web, but also, while resetting, urges the capstan in the opposite direction. The torsion springs decrease in effective diameter when the capstan is urged in the opposite direction, the friction created thereby providing braking action to prevent movement of the cylinder in the opposite direction.

United States Patent 1191 Peters [451 Nov. 25, 1975 1 1 WEB ADVANCE MECHANISM [75] Inventor:

[73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Apr. 3, 1974 [21] Appl. No.: 57,406

Kenneth Donald Peters, Jupiter, Fla.

Primary ExaminerRichard A. Schacher Attorney, Agent, or Firm-Raymond E. Smiley; Edward J. Norton ABSTRACT Web advancing mechanism suitable for use in, for example, a low cost strip printer. A pair of torsion springs surround a cylindrical capstan. A free end of each spring is attached to a member which applies torque to the springs to urge the capstan into contact with the web. An advance mechanism causes the capstan to be incrementally rotated in one direction to advance the web, but also, while resetting, urges the capstan in the opposite direction. The torsion springs decrease in effective diameter when the capstan is urged in the opposite direction, the friction created thereby providing braking action to prevent movement of the cylinder in the opposite direction.

6 Claims, 3 Drawing Figures US. Patent Nov. 25, 1975 Sheet10f2 3,921,879

US. Patent Nov. 25, 1975 Sheet20f2 3,921,879

WEB ADVANCE MECHANISM SUMMARY OF THE INVENTION contact with the web, whereby when the cylindrical means is rotated by the rotational means, the web is advanced.

' BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a printing apparatus including a preferred embodiment of the present invention;

FIG. 2 is a side elevation cross-section of the printer of FIG. 1, substantially along lines 22; and

FIG. 3 is a front elevation cross-section of the printer of FIG. 1 substantially along lines 33.

DETAILED DESCRIPTION Referring to FIG. 1, a low cost strip printer includes a generally U-shaped frame 12, to which the various members of the printer are attached. A roll of web material, such as thermal print paper 14, is rotationally supported by a shaft 16, which is coupled to frame 12 in a manner to permit removal therefrom. A spacer portion 18 of shaft 16 laterally positions the roll 14.

Referring for a moment to FIG. 2, strip of paper 20 extending from roll 14 passes under guide plate 22, under a thermal print head assembly 24 and undercapstan assembly 26 then out of the printer. Print head assembly 24 is a comercially available device that contains electrically activated bar or dot segments in contact with paper 20. When electric signals from a sig-v nal source (not shown) such as a computer are applied.

selectively to the bars or dots, they heat up causing the paper ,to discolor, thereby forming a desired pattern such as letters, numbers and symbols.

Capstan assembly 26, as seen in FIG. 1, comprises a cylindrical means or shaft 30 on a portion of which is a friction surface such as a rubber roller 32. Roller 32 is positioned to frictionally engage paper 20. Spring means comprising two identical torsion springs 34a and 34b, are positioned on shaft 30 on either side of roller 32. The inside of each spring is substantially the same as the diameter of shaft 30. The springs are wound about the shaft in a counterclockwise manner (as illustrated in FIG. 2). Therefore, when shaft 30 is rotating clockwise (as illustrated in FIG. 2), by means to be described to advance paper 20, springs 34 tend to unwind and therefore increase in diameter allowing shaft 30 to rotate freely. When an attempt is made to rotate shaft 30 counterclockwise (as illustrated in FIG. 2), the spring tends to wind up, therefore decreasing in effective diameter. This decrease in diameter causes a very large friction force to be applied to shaft 30, essentially eliminating counterclockwise motion of the shaft and therefore backwards motion of paper 20.

Each spring 34 has a tang 36 (lengended 36a and 36b respectively), which extends substantially at right angles to shaft 30. The tangs are attached to a member 38, which is rotationally mounted at each end to frame 12. A set screw 39 secures each spring to member 38.

By rotating member 38, torque is applied to shaft 30 to bias roller 32 against paper 20. When the proper adjustment has been made, fastening means, such as screws 40, are tightened to prevent rotation of the 5 torque applying member 38. Thus, springs 34 act as an anti-backlash mechanism and as a bias means for biasing roller 32 against paper 20. The springs serve yet a third purpose, namely as journal bearings for shaft 30. Side motion of the shaft is prevented by side walls 44a and 44b of frame 12 if desired tabs 46a, b, c, d, may be formed from frame 12 to further guideshaft 30. These tabs create openings 48a and 48b in side wall 44a (see FIG. 2). Similar openings (not shown) are created in side wall 44b. Tabs 46 further stabilize shaft 30 in the springs. (See FIG. 2.) The tang 52 extends through plunger 54 of a solenoid 56 and into one of a plurality of slots 58 in frame 12. Solenoid 56 is attached to a tab 60, which is bent inward from side plate 54a, creating aperture 61. A tab 62 acts as a-stop for plunger 54.

In operation, signals are applied to print head 24 to apply a desired pattern to paper 20. Then solenoid 56 is energized pulling plunger 54 upward (FIG. 2). Because spring 50 tends to tighten on shaft 30, the shaft is rotated clockwise (FIG. 2) journaled in springs 34. Because roller 32 has been biased by member 38 and springs 34 downward against paper 20, the paper is advanced. As the shaft is rotated clockwise, springs 34 tend to unwind, allowing the shaft to turn. When power is released, tang 52 of spring 50 applies a force to plunger 54 to move it away from the solenoid into stop 62. The amount of force applied to plunger 54 is a function of the slot 58 in which tang 52 is placed, an adjustment which may be made to adjust for proper operation. As plunger 54 is moved downward, it causes spring 50.to unwind, thereby releasing pressure on shaft 30. However, except for the presence of springs 34, it is likely that shaft 30 would be caused to rotate counterclockwise (FIG. 2). As explained previously,

any tendency toward counterclockwise motion of shaft 30 is prevented by the presence of springs 34, which tend to tighten.

What is claimed is:

l. Mechanism for advancing a web comprising, in

combination:

a shaft having a friction surface;

means for rotating said shaft about its axis;

spring means wound in cylindrical fashion through which said shaft passes, said spring means having a tail portion extending substantially normal to the axis of said shaft; and

means for applying torque to said tail portion for urging said friction surface of said rotating shaft into contact with said web far advancing the same.

2. Mechanism for advancing a web comprising, in combination:

a rotatable shaft having a friction surface; means for rotating said shaft in one axial direction and also capable of normally rotating said shaft in the opposite direction;

spring means wound in cylindrical fashion through which said shaft passes and which is in contact therewith over at least a major portion of a circumferential region of said shaft, said spring being wound such that as said shaft is rotated in said one direction, said spring means tends to unwind thereby increasing in effective diameter allowing said shaft to rotate freely and when said shaft is attempted to be rotated in said opposite direction said spring means tends to decrease in effective diameter creating sufficient friction with said shaft to prevent said rotation, said spring means including a tail portion extending from the wound portion of said spring in a direction substantially normal to the axis of said shaft; and

means for applying torque to said tail portion for urging said friction surface of said shaft into contact with said web whereby when said shaft is rotated in said one direction by said rotational means, said web is advanced.

3. The combination as set forth in claim 2, wherein said rotational means comprises motion creating means and an additional spring means, also through which said shaft passes, substantially similar to said first named spring means, the tail portion of said additional spring means being coupled to said motion creating means, said motion creating means creating motion in a first direction causing said additional spring means to rotate around said shaft in such a direction to decrease in effective diameter causing said shaft to rotate in said one direction, said motion creating means being thereafter caused to create motion in a second direction which would normally cause said shaft to move in said opposite direction.

4. The combination as set forth in claim 3, wherein said motion creating means is a solenoid which creates motion is said first direction, and wherein said tail portion of said additional spring means creates bias on said solenoid to cause movement in said second direction.

5. The combination as set forth in claim 2, wherein said spring means includes bearing means for permitting rotational movement of said shaft while preventing lateral movement of the same.

6. The combination as set forth in claim 2, wherein the central portion of said shaft contains said friction surface and wherein said spring means comprise two torsion springs, one on either side of said friction surface portion. 

1. Mechanism for advancing a web comprising, in combination: a shaft having a friction surface; means for rotating said shaft about its axis; spring means wound in cylindrical fashion through which said shaft passes, said spring means having a tail portion extending substantially normal to the axis of said shaft; and means for applying torque to said tail portion for urging said friction surface of said rotating shaft into contact with said web far advancing the same.
 2. Mechanism for advancing a web comprising, in combination: a rotatable shaft having a friction surface; means for rotating said shaft in one axial direction and also capable of normally rotating said shaft in the opposite direction; spring means wound in cylindrical fashion through which said shaft passes and which is in contact therewith ovEr at least a major portion of a circumferential region of said shaft, said spring being wound such that as said shaft is rotated in said one direction, said spring means tends to unwind thereby increasing in effective diameter allowing said shaft to rotate freely and when said shaft is attempted to be rotated in said opposite direction said spring means tends to decrease in effective diameter creating sufficient friction with said shaft to prevent said rotation, said spring means including a tail portion extending from the wound portion of said spring in a direction substantially normal to the axis of said shaft; and means for applying torque to said tail portion for urging said friction surface of said shaft into contact with said web whereby when said shaft is rotated in said one direction by said rotational means, said web is advanced.
 3. The combination as set forth in claim 2, wherein said rotational means comprises motion creating means and an additional spring means, also through which said shaft passes, substantially similar to said first named spring means, the tail portion of said additional spring means being coupled to said motion creating means, said motion creating means creating motion in a first direction causing said additional spring means to rotate around said shaft in such a direction to decrease in effective diameter causing said shaft to rotate in said one direction, said motion creating means being thereafter caused to create motion in a second direction which would normally cause said shaft to move in said opposite direction.
 4. The combination as set forth in claim 3, wherein said motion creating means is a solenoid which creates motion is said first direction, and wherein said tail portion of said additional spring means creates bias on said solenoid to cause movement in said second direction.
 5. The combination as set forth in claim 2, wherein said spring means includes bearing means for permitting rotational movement of said shaft while preventing lateral movement of the same.
 6. The combination as set forth in claim 2, wherein the central portion of said shaft contains said friction surface and wherein said spring means comprise two torsion springs, one on either side of said friction surface portion. 